1. Field
The present invention concerns Bluetooth communications, and more particularly, a method and system for optimizing Bluetooth transmissions to overcome signal interference.
2. Description of Related Art
“Bluetooth” is a wireless personal area network technology supporting wireless voice and data communication between different nearby devices. A number of different devices can be Bluetooth-enabled, for example, cell phones, personal digital assistants, or laptop computers. Each such device is equipped with a receiver, transmitter, and other Bluetooth components, allowing it to communicate with other similarly equipped devices nearby without the use of cables or other physical connections.
Bluetooth enabled devices (“Bluetooth devices”) operate in the unlicensed 2.4 GHz ISM (“Industrial, Scientific and Medical”) band, which spans a frequency range of 2400.0 to 2483.5 MHz in the United States and Europe. The ISM band is further divided into 80 RF channels or frequency bins, which are each 1.0 MHz wide.
In addition to Bluetooth devices, the ISM band is also occupied by systems that operate under the IEEE 802.11 b specification for wireless local area networks (“IEEE 802.11b wireless systems”). Other devices such as microwave ovens also operate in the same ISM band. IEEE 802.11b wireless systems and microwave ovens operate in the ISM band at much greater transmit power than Bluetooth devices. Thus, due to the overlapping frequency bands and greater signal strength utilized by some non-Bluetooth devices, there is a possibility of such devices interfering with Bluetooth communications.
Signal interference is undesirable for various reasons. Chiefly, signal interference can cause Bluetooth transmissions to fail, requiring time-consuming retransmission at the expense of additional power consumption. Since many Bluetooth devices operate on battery power, greater power consumption is undesirable because it drains the battery more quickly. Ultimately, the battery must be recharged, or if a recharging source is unavailable, the battery will cease to operate. As another disadvantage of signal interference, retransmission of Bluetooth signals increases the possibility of causing interference for other Bluetooth and/or IEEE 802.11 b wireless systems operating in the same area. As still another disadvantage, signal interference can reduce the quality of real-time, streaming data, causing a garbled or low quality signal. For various reasons, then, signal interference in Bluetooth communications is undesirable.
To avoid interference from other devices operating in the ISM band, the Bluetooth system uses a technique known as “frequency hop spread spectrum.” In frequency hop spread spectrum, inter-communicating Bluetooth devices hop to a different frequency after each transmission and reception, at a rate of 1600 hops per second. Thus, transmitting and receiving at a different frequency 1600 times per second reduces the probability of the Bluetooth devices encountering long lasting signal interference in one particular frequency bin.
The following approach has been developed to further reduce potential interference to Bluetooth communications. Here, the Bluetooth devices identify the particular ISM frequency bins where interfering devices are radiating or transmitting. The inter-communicating Bluetooth devices then agree to avoid transmitting and receiving on those particular bin frequencies. However, this approach requires governmental approval from the Federal Communications Commission, which currently does not allow devices operating in the ISM band to coordinate transmissions of two radios by selecting fixed frequency subsets.
Another approach is mentioned in a white paper published by Texas Instruments, entitled “Wi-Fi (IEEE 802.11b) and Bluetooth,” by Matthew B. Shoemaker, February 2001, Version 1.1. The Shoemaker paper recognizes that various mechanisms can be used to improve the coexistence level of Bluetooth devices when interference is present. For data connections, Shoemaker proposes that Bluetooth devices adaptively select the type of error control used and the length of each packet to transmit in order to maximize the throughput. In addition, Shoemaker proposes flow control to dynamically increase and decrease the rate of transmission. For example, when a contiguous block of bad channels is reached, the Bluetooth device places traffic on hold until good channels are available. Nonetheless, the Shoemaker paper lacks practical details of how to implement these concepts.
Consequently, known Bluetooth communication systems are not completely adequate in all respects due to the unsolved problem of signal interference.